Loudspeaker diaphragm and method of fabricating the same



y 1942- t E. J. WlEST 2,282,839

LOUDSPEAKER DIAPHRAGM AND METHOD OF FABRICATING THE SAME Filed July 31, 1940 Fi e. 1.

'FJ'IG. 3.

3maentor Edward J Wiest Patented May 12, 1942 Edward J. Wlest, Oak Lane, Pa., assignor'to Radio Corporation of America, New York, N. Y., a

corporation of Delaware Application July :1, 1940, Serial No. 348,862

Claims.

for loudspeakers, and more particularly to the method of fabricating the same.

It has long been recognized that, in loudspeakers of the electrodynamic type, it is desirable to place a dust cap over the hollow voice coil form to prevent dust from entering into the air-gap between the coil form and the magnet structure. The customary practice is to form the dust cap separately from the diaphragm and to apply the cap to the voice coil form after the form has been secured to the diaphragm.

It has also been customary to form diaphragms out of paper'flock by a felting process in which the fibres are suspended in water and are sucked onto a preformed screen to give the diaphragm the desired shape. One such form or screen is so shaped that a hollow, central projection is provided on the diaphragm through which the voice coil form may be inserted for attachment to the diaphragm. The end of this projection is closed ofl during the felting process, and this end must, obviously, be cut oil in orderto permit insertion of the voice coil form. Heretofore, these ends have been discarded and separate dust caps have been fabricated to place over one end of the voice coil form, thus necessitating additional expense and additional manufacturing steps and material, a substantial part of the felted diaphragm going to waste.

Gil

(Cl. its-115.5)

This invention relates to acoustic diaphragms' the same diameter as this flange and therefore fits snugly over the end of the voice coil form. In this way, the manufacture of separate dust caps and waste of diaphragm material are eliminated, and an eflicient diaphragm is provided.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to the method in which it may be practiced and the resulting diaphragm, together with additional objects and advantages thereof, will best be understood from the following description of one embodiment thereof, when read in connection with the accompanying drawing, in which Figure 1 is a view, partly in section, of a felted diaphragm after it has been removed from the felting apparatus and dried,

Figure 2 is a similar view with the cap member severed from and in separated relation to the attaching flange on the diaphragm,

Figure 31a an enlarged sectional view showing the voice coil form in place on the diaphragm,

The primary object of my invention is to pro- I vide an improved method of fabricating diaphragms of the type set forth which are not subject to the aforementioned defect.

More particularly, it is an object of my invention to provide a novel'method of manufacturoutwardly extending, central, hollow, cylindrical projection 3 having a closed end 5. As the first step in practicing my invention after the diaphragm I has been formed, the projection 3 may be cut or severed along a plane intermediate its ends and normal to its axis. Such a plane is designated by the dash line AA in Fig. 1. When 40 this step has been completed, the resulting diajection of which the diaphragm is originally formed, I employ this end portion as a cap member and place it over one end of the voice coil form after the latter has been secured to the diaphragm. Obviously, since the cap is cut of! from the cylindrical projection or flange through which the voice coil form is inserted and to which it is phragm l is provided with an outwardly extending, central, open ended flange 3a and a capmember having the closed end 5 and a cylindrical surface 3b which is a continuation of and therefore has the same diameter asthe flange 3a.

A tubular, cylindrical voice coil form I on which may be wound one or more turns of wire to form a suitable voice coil 9 is next inserted through the opening of the diaphragm provided by the flange 3a. The external diameter of the voice coil form I is preferably the same as the internal diameter of the flange 3a, and it is secured to the flange 3a in any suitable way, as by cement or varnish. Preferably, the voice coil form 1 extends through cemented or otherwise suitably secured, it has e fl g to a p in Where the end 4 hereof, adjacent which the coil I is wound, lies on one side of the diaphragm and its opposite end 'lb is on the opposite side of the diaphragm. After the voice coil form I has been secured in place, the cap member may be fitted over the end lb thereof and secured thereon by cement or the like. The fiange ID of the cap member being of the same diameter as the fiange is left on the diaphragm I, it is obvious that the cap member will "fit snugly over the coil form I, the end I of the cap member completely closing the end lb of the voice coil form and therefore acting as a dust cap therefor.

Although I have shown and described but one embodiment of my invention, it will be obvious to those skilled in the art that a number of variations may be made therein. For example, instead of making the projection 3 extend outwardly of the frusto-conical diaphragm I, it may be made to extend inwardly, and the same process as above described may be carried out with respect to it. Also, instead of winding the coil I on the end Id of the voice coil form, it may be wound on the end lb thereof and the dust cap placed over the end Id of the coil form. Other similar changes will, no doubt, readily suggest themselves to those skilled in the art. I therefore desire that my invention shah not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims,

I claim as my invention:

1. The method of fabricating a frusto-conical acoustical diaphragm which comprises forming the diaphragm with a closed, hollow, outwardly extending projection on its apex end, removing the closed end of said projection to provide the diaphragm with an opening, inserting a voice coil phragm. and finally applying said cap member over one end of said form and securing said cap member thereto.

3. The methodof fabricating a frusto-conical acoustical diaphragm which comprises forming the diaphragm with a hollow, outwardly extending projection on its apex end the outer end of which is closed, severing said projection along a plane substantially normal to the axis of said projection to provide an opening through said diaphragm and to provide a cap member constituted by said outer, severed end, inserting a tubular voice coil form through said opening and securing said form to said diaph asm, and finally fitting said cap member over" one end of said form and securing said cap member thereto.

4. The method of fabricating a frusto-conical acoustical diaphragm which comprises forming the diaphragm with a hollow, outwardly exber over one end of said form and securing said cap member thereto.

5. .The method of fabricating a frusto-conical acoustical diaphragm which comprises form ing the diaphragm with a substantially central, hollow, outwardlyeextending cylindrical projection on its apex end which is closed at its outer end, severing said projection intermediate its ends along a plane substantially normal to its axis whereby to provide an annular flange on said diaphragm defining an opening therethroush and a severed cap member also having an annular fian'g'e which is a continuation of said first named fiange, inserting a cylindrical voice coil form through said opening and securing said form to said first named flange, and finally fitting said cap member over one end of said form and secur ing said second named fiange thereto whereby to fix said cap member to said form.

EDWARD J. WIEST. 

